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Rare earth oxides are used in the fabrication of dense silicon nitride (Si(3)N(4)) components. These oxides react at high temperatures with SiO(2) (present on the surface of all commercial Si(3)N(4) powders) to form a liquid phase which allows densification by particle rearrangement and solution-reprecipitation. The remaining liquid solidifies and a number of phases, both crystalline and glassy, form. The oxidation behaviour of the intergranular phase plays a significant role at temperatures below 1100 C as oxidation is often accompanied by molar volume increases. At these temperatures, Si(3)N(4) itself is hardly oxidised. This paper deals with the oxidation of N-alpha-Wollastonites (MSiO(2)N). Dense Y and Ce Wollastonite (K-phase) were prepared by hot pressing and gas pressure sintering, respectively. Specimens were exposed to dry synthetic air and the reactions were monitored using hot stage microscopy and thermogravimetric analysis. XRD and WDS were used to analyse the materials and oxidation products.

Additional information

Authors: O'REILLY M, JRC Petten (NL);FORDHAM R, JRC Petten (NL);NORTON J, JRC Petten (NL);BULLOCK E, JRC Petten (NL);CORISH J, University of Dublin, Trinity College (IE)
Bibliographic Reference: Paper presented: 6th International Conference on Intergranular and Interphase Boundaries in Materials, Thessaloniki (GR), June 22-26, 1992
Availability: Available from (1) as Paper EN 36919 ORA
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